Present day data communication systems, both wireless and wire-line, have a requirement to transfer data between communication units. Data, in this context, includes many forms of communication such as speech, multimedia, signalling, etc. Typically, such data communication needs to be effectively and efficiently transported, in order to optimise use of limited communication resources.
Due to the recent growth in communications, particularly in Internet and wireless communications, there exists a need to provide improved data transfer techniques, where a particular quality of service of the transmitted data is often required or desired by the end user.
The European Telecommunication Standards Institute (ETSI) has defined a number of communication standards with the aim that a number of manufacturers are able to provide equipment that supports the same technology and are able to inter-operate with other equipment compliant with that standard. One such data communication standard developed by ETSI is the terrestrial digital video broadcasting (DVB-T) standard (ETSI EN 300 744), which has been developed for digital television sets and set-top boxes.
A recent variation of the DVB-T standard that has been adopted to incorporate enhanced features to allow improved reception of digital video broadcasting services for mobile devices is the digital video broadcasting-handset DVB-H standard. A DVB-H unit is battery powered, and the nature of the broadcast transmission offers a possibility to the DVB-H unit to repeatedly power off components/circuits of the DVB-H unit's receiver chain to increase battery usage. It is anticipated that DVB-H units may receive transmissions at a variety of locations, such as: indoor, outdoor, as a pedestrian, within a moving vehicle, etc.
One feature that has been incorporated within the DVB-H standard that facilitates this aim of mobile reception is the use of multi protocol encapsulated-forward error correction MPE-FEC of received data. MPE-FEC facilitates recovery of data by a receiver in situations of high data-packet loss, which can occur when a receiver is in a changing environment, for example when a receiver is moving. MPE-FEC regroups data into blocks (MPE-FEC frames) and performs forward error correction on these data blocks. For an efficient error correction mechanism, a common approach is to have MPE-FEC frames larger than 512 Kbits. Thus, a receiver operating within a DVB-H compatible system receives an MPE-FEC frame with up to 2 Mbit of data over a single channel in a relatively short time period, for example 200 millisecond.
To save power, the DVB-H standard has incorporated a technique of ‘time-slicing’. Time slicing is a mechanism that regroups data into bursts. A burst is a quantity of data that is sent in a small amount of time. The next burst is sent after a significant time delay, and so on. During this period of time, bursts from other programs or applications are sent. In this manner, the receiver is only activated when there is a burst. Generally, within the DVB-H standard, bursts and MPE-FEC frames correspond. This means there are an integer number of complete MPE-FEC frames per burst.
It is known that a unidirectional delivery of data may be distributed between several logical channels, in order to enable receivers to more accurately specify the metadata (i.e. data that describes the content, condition of access and/or other characteristics of data) that the receivers are interested in. In this manner, a receiver needs only to access the logical channels of interest. Thus, the receiver is able to reduce an amount of time, storage and/or CPU resources needed for processing the data when a unidirectional delivery mechanism is used. Also, hierarchical channels enable receivers to subscribe to a, possibly well known, root multicast channel/group and progressively access only those additional channels.
Data carousel is a known mechanism that repetitively sends a set of data files over a data communication network. By repeating the transmission of data items/files within the set, any receiving communication unit needs only to receive the transmission over a single ‘cycle’, to ensure that each item of data is received. A server, generally located within the communication network, sends each file individually. Thus, when the server has sent the last file, the server then restarts sending the first file. This methodology has led to the common terminology of ‘Data carousel’.
Thus, at the receiving side of a data network employing a data carousel methodology, there is no notion of a first and a last file as the transmission is cyclic. In this manner, in order to receive a file on one carousel, a user potentially has to wait for all of the files to arrive, in order to obtain a particular data file.
Therefore, the server transmits each file in the data carousel in turn and then restarts the transmission once a transmission cycle is complete. However, as the data content becomes richer, the size of files on the data carousel increases to such an extent that transmission time becomes excessive.
By way of explanation, in the context of data information relating to the world-wide-web (www), an item of information may be a document that may contain textual information and/or illustrations in the form of multimedia content. There are many instances where multimedia information on an information page is updated regularly, with the result that one or more data items are changed on the web page. In this context, the document generally needs to be sent every few seconds.
Furthermore, particularly in the context of web pages, a content provider typically wants their document to look attractive. Therefore, the content provider will often add multimedia content in the form of attractive images, flash movies, etc. The addition of such multimedia content significantly increases the size of the complete document, which can typically require up to several MBytes in current data systems. Therefore, there is a need to deliver large amounts of data content in an efficient manner.
In addition, in a wireless environment, bandwidth is expensive. Content Providers who provide electronic service guides (ESGs), such as television guides, do not want to allocate large amounts of bandwidth to the broadcasting of such documents.
In the art of data carousel networks, a paper by OtaDigi Herrero, C. Cesar, P. and Vuorimaa, P., published in the 6th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Service, volume: 1, 1-3 Oct. 2003, discloses on pages: 231-234 an optimized carousel configuration technique. The proposed technique discloses a method whereby files required at a starting phase of a carousel operation are sent into the object carousel five times more often than a typical carousel operation. In particular, the paper discloses a mechanism of hierarchical data separation, with custom transport parameters, a custom repetition rate for the starting phase and caching of HTML EPG files for faster display.
Thus, a need exists for a mechanism, for example within a DVB-H receiving unit, to more efficiently deliver data content using a data carousel methodology.